是的，如mongoose文档www.example.com中所述，可以跨数据库填充https://mongoosejs.com/docs/populate.html#cross-db-populate
无论是在父模式中引用模型示例（示例1），还是执行实际的填充（示例2），您都需要访问模型示例。

文档中的示例1-定义事件模式时使用模型示例：

const db1 = mongoose.createConnection('mongodb://127.0.0.1:27000/db1');
const db2 = mongoose.createConnection('mongodb://127.0.0.1:27001/db2');

const conversationSchema = new Schema({ numMessages: Number });
const Conversation = db2.model('Conversation', conversationSchema);

const eventSchema = new Schema({
  name: String,
  conversation: {
    type: ObjectId,
    ref: Conversation // `ref` is a **Model class**, not a string
  }
});
const Event = db1.model('Event', eventSchema);

//You can then perform a regular population as if they are on the same DB
const events = await Event.find().populate('conversation');

文档中的示例2-在执行填充时使用模型示例：

const db2 = mongoose.createConnection('mongodb://127.0.0.1:27001/db2');

const conversationSchema = new Schema({ numMessages: Number });
const Conversation = db2.model('Conversation', conversationSchema);

//Then pass the model instance as an option to populate() 
const events = await Event.find().populate({ path: 'conversation', model: Conversation });